DATA TRANSMISSION METHOD AND DATA TRANSMISSION SYSTEM IN A CELLULAR RADIO NETWORK

Abstract: A data transmission method in a cellular radio system, comprising as network elements a base station controller and base stations connected in series thereto via data transmission links; in the method, data is transmitted over said data transmission links in frames divided into timeslots. To control the data transmission network formed by the data transmission links, configuration data (308) indicating in which timeslots of the frame the useful data (302) intended for the network element is carried is transmitted to the network element in a predetermined timeslot (308) of the frame.

Description: Data transmission method and data transmission system in a cellular radio network. Field of the Invention The invention relates to a data transmission method and a data transmission system in a cellular radio system, comprising as network elements a base station controller and base stations connected in series thereto via data transmission links; in the method, data is transmitted over said data transmission links in frames divided into timeslots. Background of the Invention In cellular radio systems, it is known to con- nect a plurality of base stations in series with one another by means of data transmission links in such a way that a plurality of base stations are controlled by one base station controller. The base station controller transmits data to each base station through other base stations in a certain predetermined timeslot of the data transmission link. These timeslots are fixed, i.e. the incoming and outgoing traffic of a base station are always carried in the same timeslot/timeslots. Fig. 1 shows a block diagram in which a Base Transceiver Sta- tion BTS 1 is connected to a Base Station Controller BSC. Fig. 2 shows base stations BTS 1, BTS 2 and BTS 3 connected in series in such a way that they communicate with the base station controller BSC through one another. An example for data transmission links used for carrying traffic between the base stations of a cellular radio network is a so-called Abis interface described in the GSM recommendations "GSM 12.21, 1992, Network Management Procedures and Messages on the Abis Inter¬ face, ETSI" and "GSM 08.54, 1992, BSC-BTS-Layer 1 Speci- fication, ETSI". The Abis interface is divided into timeslots in the manner shown in fig. 9. The interface may have e.g. 32 timeslots of 64 kbit/s. When it has been necessary to change, e.g. increase, the amount of data transmitted to the base station, it has been pos- sible to allocate a plurality of timeslots of a data transmission link to a specified base station. This has been implemented such that the base station controller has started to transmit data to each base station in a new timeslot and the base stations have been moved to receive incoming data from the correct timeslots. Typic¬ ally, the base stations have been moved to receive data transmitted in the correct timeslots by manually modify¬ ing the configuration data of the data transmission link in the files of each base station. In the above solution of the prior art, the number of data transmission links between the base sta¬ tions of the network, i.e. the configuration of the network, can be modified only manually in such a way that the maintenance personnel checks on all the base stations to be modified and allocates the timeslots needed by means of the operation and maintenance unit of each base station. This is laborious, and if one data transmission link of a network formed by a plurality of base stations is allocated wrong, it may be necessary to re-configure the entire system. In this kind of prior art system, it is impossible to flexibly modify the network structure, i.e. the transmission capacity alloc¬ ated for connections between different base stations and base station controllers or switching centres. It is thus impossible to modify the transmission capacity of the different base stations e.g. daily, depending on, for example, which base station has the heaviest traffic load. This kind of characteristic would be very useful for mobile phone operators in urban and suburban areas. When a system is used in which transmission capacity can be flexibly allocated to different base stations, the operators are not charged for the maximum transmission capacity between the base stations and the base station controller or switching centre, since it is possible to allocate transmission capacity for each connection in the amount needed. Another drawback of the prior art system is that due to manual configuration of the trans¬ mission links of the network, it is difficult to manage the network described in the prior art since the network cannot be managed from one point but each base station must be checked on separately when the configuration of the network is to be modified. Further, it is difficult for the system described in the prior art to recover from a fault since a faulty timeslot cannot be flexibly replaced by another timeslot and since a faulty connec¬ tion e.g. in a ring-formed base station network cannot be replaced by establishing another transmission link to the base station from the other direction of the ring. Disclosure of the Invention The object of the present invention is to pro¬ vide a data transmission method and system by which the above problems of the prior art can be avoided. The object of the invention is also to enable flexible allocation of data transmission links between the base stations of the cellular radio network in such a way that the timeslots of the data transmission links can be flexibly allocated to different base stations. The object of the invention is thus to automate and facilit¬ ate the setting up or configuration of the structure of the data transmission network between the base station and the base station controller or switching centre. This new kind of data transmission method is achieved with the method of the invention, which is characterized in that configuration data indicating in which timeslots of the frame the useful data intended for the network element is carried is transmitted to the network element in a predetermined timeslot of the frame. Further, the data transmission system according to the invention is characterized in that configuration data indicating in which timeslots of the frame the useful data intended for the network element is carried is transmitted to the network element in a predetermined timeslot of the frame. The basic idea of the invention is that a cer¬ tain channel, typically a timeslot, is assigned for network management. The configuration data, i.e. the data by means of which the base stations find the data channels, typically voice channels, allocated to them are transmitted to the base stations on this network management channel. Another basic idea of the invention is that all the base stations look for configuration data intended for them in the same predetermined time¬ slot, and in the base station network a preceding base station places the configuration data intended for the following base station in that same predetermined time¬ slot. This predetermined timeslot may be the last time- slot of the frame on a data transmission link, whereby the data stream passing through the base station is redivided such that the base station that is logically the following base station in the network finds the control data intended for it in the last timeslot intended for it. The advantage of a data transmission method and system according to the present invention is that according to the method and system of the invention, the structure of the base station network, i.e. the number of the transmission lines allocated to each base station and their location over the transmission link, can be changed quickly and without any difficulties. This can be performed when considered necessary, and especially when the loading of the base stations varies and the number of the transmission links allocated to them is to be changed. Another advantage of the invention is that a base station is quicker and easier to install in the network since the person installing the base station need not program the base station on the spot as part of the network but the system automatically connects the base station to the network. Also, since the network can be managed and the configuration of the transmission links between the base stations modified by the base station controller or switching centre in a centralized manner, the work of the person installing the base station is essentially facilitated. The installer of the base station need not be familiar with the structure of the whole base station network. Also, the method and system according to the invention reduce occurrence of faults and malfunctions in the base station network. An advantage of the invention is that the structure of the base station is easier to control. The data about the structure of the base station can thereby be displayed on the base station controller and the configuration of the network can be easily changed from one point in the network. Another advantage of the method and system according to the invention is that certain failures occurring in the network can be quickly and reliably overcome by the automatization and concentration of the network management according to the invention. For example, if the configuration data is always placed in the same predetermined timeslot, a base station in the network can always easily detect the configuration data intended for it in the same timeslot. If a link in a ring-formed network is disconnected, the configuration data of the network can then be transmitted to the opposite direction in the network, and thus the base station network can be re-configured and it starts to operate again despite the disconnection of the link. Another advantage of the invention is that a base station network operating in accordance with the invention needs less transmission capacity for alloca¬ tion of data channels, such as voice channels, between the base stations and the base station controller or switching centre. Brief Description of the Drawings In the following the invention will be described in greater detail with reference to the attached drawings, wherein Fig. 1 shows a block diagram of a base station controller and a base station connected thereto via a data transmission link, Fig. 2 shows a block diagram of a base station controller and of base stations connected in series thereto via a data transmission link, Fig. 3 shows a schematic view of a data trans¬ mission frame of the invention over a data transmission link between a base station controller and a first base station, Fig. 4 shows a schematic view of a data trans- mission frame of the invention over a data transmission link between a first and second base station, Fig. 5 shows a schematic view of allocation of data transmission channels to different base stations, Fig. 6 shows a block diagram and a functional diagram of a data transmission system and method accord¬ ing to the invention, Fig. 7 shows a schematic view of cross-connec- tion of timeslots, Fig. 8 shows as a flow diagram how the con¬ figuration of a data transmission network according to the invention is modified, Fig. 9 shows a schematic view of the frame structure of an Abis interface, Fig. 10 shows a schematic view of a base sta¬ tion network to which the base stations are connected via their transmission means, Fig. 11 shows a flow diagram of the configura- tion of a base station network. Detailed Description of the Invention Figs. 1 and 2 are described above at the begin¬ ning of the specification. Fig. 3 shows a frame structure of a data trans¬ mission link between a base station controller and a first base station. In the frame shown in Fig. 3, the link managing information is placed e.g. in a first timeslot 301. The following timeslots contain first the calls or other data 302 intended for the first base station BTS 1. The following timeslots contain the use¬ ful data, such as calls, intended for the second 303 base station BTS 2 and the third 304 base station BTS 3. The following field 305 is not in use, and the field 306 contains the configuration data used by the third base station BTS 3; on the basis of this data the third base station detects the useful data intended for it, placed in the field 304. The field 307 contains the configuration data intended for the second base station BTS 2, by which the second base station BTS 2 detects the useful data intended for it, placed in the field 303. Further, the field 308 contains the configuration data intended for the following base station, i.e. the first base station BTS 1; by this data the first base station detects the useful data 302, such as a voice channel, intended for it. The configuration data intended for the following base station is always placed in this last timeslot or field 308. Naturally, some other field or timeslot of the frame could also be assigned as the unchangeable predetermined field. It is also possible to modify the structure of the entire data transmission frame between the base stations dynamically such that all data contained in the data transmission frame is placed in a new position in the frame at each base station. Further, it is also possible to mark with an identifier the timeslot or field in which the con¬ figuration data to be transmitted is placed. It is then sufficient to transmit these identifiers to the follow¬ ing base station, and the following base station is able to detect the configuration data intended for it in the frame transmitted and to use the data for searching and detecting the data, e.g. voice channels, intended for it. Fig. 4 shows a schematic view of a data trans- mission frame of the invention over a data transmission link between the first BTS 1 and second BTS 2 base sta¬ tion. The fields 301, 303, 304, 305 and 306 of the frame to be transmitted are the same as those of the data transmission link described above, i.e. they correspond to the fields of Fig. 3. A new feature as compared with the above data transmission link is that the calls (or other data) transmitted to the first base station BTS 1 have been removed from the field 302, and the field 401 is thus not in use. Naturally, something else could have been placed therein. The most significant change in regard to the above transmission link is that the field 308 does not contain the configuration data trans¬ mitted to the base station 1 but that the base station 1 BTS 1 has placed therein the configuration data intended for the base station 2 BTS 2. Further, the field 307 in which the configuration data intended for the second base station BTS 2 was placed on the first transmission link is not in use 402 or some other data may have been placed therein. The basic idea of the invention is that the first base station collects the configuration data intended for it from a predetermined field or timeslot and disposes the configuration data needed by the following or second base station in that same field, the configuration data informing the base station in which part of the frame the useful data, such as a voice channel, intended for it is located. Fig. 5 shows a database of a base station con¬ troller BSC or possibly of a switching centre of a cellular radio system. In this database the user has defined the call capacity intended for each base sta¬ tion. A network configuration entity (shown in Fig. 6) located in the base station controller BSC transmits to each base station transmission means that-* contacts it the configuration data needed by that particular base station. On the basis of the configuration data the base station concerned detects the call or other data intended for it in the frame structure of the Abis interface. The table shows it to the configuration entity of the base station controller how much trans- mission capacity it must allocate for traffic between itself and each base station. Fig. 6 shows the elements needed in automatic configuration of a base station network. According to the invention, when the current is switched on in base stations BTS 1 601 and BTS 2 602, the base stations try to establish a connection with the base station controller BSC 600 through the Abis network. At first only the first base station BTS 1 manages to establish a connection since it uses a predetermined channel. The predetermined channel may be e.g. the last channel of the frame. In the base station controller, transmission of configuration data to the base stations is controlled by a network configuration entity 604. The base station controller BSC responds to the first base station on this channel. The other base stations are not able to establish a connection since BTS 1 is not yet ready to pass data to them. The base station controller BSC transmits to BTS 1 the configuration data intended for it, the configuration data comprising the list of Abis timeslots intended for the first base station and data for other base stations about cross-connection of time¬ slots intended to be performed by that particular base station. The table 603, which contains this data, is e.g. of the type described in Fig. 7. It is seen there- from that the second base station BTS 2 receives the configuration data it needs in a timeslot 32 allocated to it for operation and maintenance O&M signalling, and is thereby able to establish a connection with the base station controller BSC 600. The cross-connection can be performed in either direction: for BSC -> BTS connec¬ tion, 31 is connected to the channel 32, and for BTS -> BSC, vice versa. The corresponding configuration data including the cross-connection table is then transmitted to the second base station BTS 2. The last BTS of the network does not need cross-connection data: when base stations are connected in series, the last base station is (logically) not followed by a base station that would require cross-connection. Further, the cross-connection may be a free cross-connection, which means that any timeslot can be transferred to any other timeslot when the data stream passes through the transmission means. Transmission means 606, 608 is the unit of the base station 601, 602 that allocates Abis channels (timeslots) to the base station and performs the desired cross-connection of the data stream passing through the base station to the other base stations. Transmission means of this kind are already available. Fig. 6 also shows that calls and operation and maintenance data O&M are passed through the transmission means 606 to the first base station BTS 1 601. The corresponding data is transmitted to the second base station BTS 2. The base stations of a cellular radio network can be connected such that they form a ring, to ensure that the connection between the base station controller BSC and the base stations BTS is maintained although the connection from one direction fails. Data can then be transmitted by using the other connection of the base station ring. In Fig. 6, the connection of the base stations such that they form a ring is indicated by reference number 609. Whether or not the connection between the base stations and the base station control¬ ler is maintained depends on where the base station ring breaks. Fig. 8 shows a flow diagram for the configura¬ tion of the base station network. In the first step, the current of the base stations of the network is switched on 801. Then the first base station BTS 1 informs 802 the base station controller BSC that it is ready for configuration. The first base station performs the con¬ figuration by using the channel 32, i.e. the last chan¬ nel of the frame or an otherwise fixed channel. The base station controller BSC then configures 803 the first base station BTS 1 by using the channel 32. The Abis transmission means of the base station BTS 1 is then initialized to collect the desired channels from the desired timeslot for the first base station, and to transfer to the following base station or base stations the channels needed by them. Being able to signal with the base station controller BSC on the A-bis channel 32, the base station BTS then establishes a connection 804 with the base station controller BSC. The other base stations BTS are then initialized 805 on the same prin- ciple, and after this the base station network is ready 806 to operate. If the configuration of the network is to be modified when the network is already in operation, this can be performed on the above principle, starting with the base station whose voice channel number is to be changed. Fig. 9 shows a schematic view of a frame struc¬ ture of an Abis interface. The transmission rate of the Abis interface is e.g. 2 Mbit/s, divided into 32 time¬ slots of 64 kbit/s. In the solution of the invention, the transmittable network configuration data is placed in a predetermined timeslot, such as here the last time¬ slot, which is used for transmitting operation and main¬ tenance data to the base stations. Fig. 10 shows a schematic view of a base sta- tion network to which base stations 1001 and 1003 are connected by their transmission means 1002 and 1004. If necessary, the transmission means reorganizes the 64 kbit/s timeslots located in the 2 Mbit/s frame of the Abis interface. This takes place as the frame "passes" through the transmission means. The order in which the base station puts the timeslots that have passed through it is determined by configuration, i.e. by giving the necessary configuration data to the transmission means e.g. on the operation and maintenance channel of the transmission link. Fig. 11 shows a flow diagram of the configura¬ tion of a base station network. In step 1101 the network user designs a configuration table for the network. The base station controller BSC then transmits 1102 the configuration data needed by the nearest base station to the transmission means of that base station in a predetermined timeslot, e.g. in the timeslot allocated for operation and maintenance. The first base station then operates in a way as a repeater and transmits to the following base station the configuration data trans¬ mitted by the base station controller. In other words, the base station controller BSC transmits 1103 the con¬ figuration data needed by the following base station to said base station. The drawings and the description thereof are to be understood only as illustrating the idea of the invention. The data transmission method and system of the invention may vary in their details within the scope of the claims. Although the invention is described above mainly as applied to a GSM system, it may also be used in other cellular radio systems. With regard to the modifications of the invention, it should especially be noted that any timeslot can be permanently assigned as the timeslot used for transmission of configuration data. In the present example this timeslot is the last timeslot available, but it may also be any other time¬ slot and even vary from one base station to another, as long as each base station receives information indicat¬ ing where the configuration data intended for it is located. However, in the beginning the timeslot must be fixed; otherwise it would not even be possible to send network configuration commands to a base station and the base station would not be able to receive them. In one alternative embodiment of the invention the base station BTS can also configure the Abis inter- face or transmission means without the help of the base station controller BSC. The automatization degree of the invention can thus be raised at the base stations. Each base station then makes a certain initial setting, which the base station controller BSC can later modify base station-specifically, if necessary.

Claims: Claims 1. A data transmission method in a cellular radio system, comprising as network elements a base station controller (BSC) and base stations (BTS 1, BTS 2) connected in series thereto via data transmission links; in the method, data is transmitted over said data transmission links in frames (Fig. 9) divided into timeslots; and the method is c h a r a c t e r i z e d in that configuration data (308, 403) indicating in which timeslots of the frame the useful data (302, 303, 304) intended for the network element is carried is transmitted to the network element in a predetermined timeslot (308, 403) of the frame. 2. A data transmission method according to claim 1, c h a r a c t e r i z e d in that on the basis of said configuration data (308, 403), the network elements (BTS 1, BTS 2) receiving the data collect the useful data (302, 303, 304) intended for them from different timeslots of the frame. 3. A data transmission method according to claim 1 or 2, c h a r a c t e r i z e d in that said configuration data (308, 403) indicating in which time¬ slots the useful data (302, 303, 304) intended for the network element is carried is placed in the operation and maintenance channel that is transmitted over the data transmission link and is used for otherwise con- trolling the base station. 4. A data transmission method according to claim 1, 2 or 3, c h a r a c t e r i z e d in that said configuration data (308, 403) is placed in the last timeslot of the frame on the data transmission link. 5. A data transmission method according to claim 1, 2, 3 or 4, c h a r a c t e r i z e d in that said configuration data (308 ) intended for each network element (BTS 1, BTS 2) is transmitted to a first network element (BTS 1 ) in a predetermined timeslot (308) of the frame, and the configuration data indicating in which timeslot of the data transmission link the useful data (303) intended for a second (BTS 2) network element is carried is transmitted to the first network element in another timeslot (307) of the frame, whereby the con- figuration data indicating in which timeslot of the data transmission link the useful data intended for the sec¬ ond network element is carried is transmitted from the first network element to the second network element in said predetermined timeslot (403) of the frame. 6. A data transmission method according to claim 5, c h a r a c t e r i z e d by the following steps: a first network element (BTS 1 ) receives con¬ figuration data indicating in which timeslot the useful data (302) intended for the first network element is carried in a predetermined timeslot (308) , and config¬ uration data indicating in which timeslot the useful data (303) intended for the second network element is carried in another timeslot (307) ; the first network element (BTS 1) transfers the configuration data (307) indicating in which timeslot the useful data (303) intended for the second network element (BTS 2) is carried from the second timeslot (307 ) to the predetermined timeslot (308) ; the first network element (BTS 1) transmits the configuration data indicating in which timeslot the useful data (303) intended for the second network element is carried to the second network element (BTS 2) in a predetermined timeslot (403) . 7. A data transmission method according to claim 1, 2, 3, 5 or 6, c h a r a c t e r i z e d in that on the data transmission link between a first net¬ work element (BSC) and a second network element (BTS 1) said configuration data is placed in the first timeslot marked with an identifier, and on the data transmission link between the second network element (BTS 1 ) and a third network element (BTS 2) , in the second timeslot marked with an identifier. 8. A data transmission method according to claim 7, c h a r a c t e r i z e d in that the identi¬ fier of said first timeslot marked with an identifier is transmitted to the first (BSC) and second network element (BTS 1), and that the identifier of said second timeslot marked with an identifier is transmitted to the second and third (BTS 2) network element. 9. A data transmission method according to any one of the preceding claims, c h a r a c t e r i z e d in that the configuration data intended for each network element and transmitted between a first (BTS 1) and second network element (BTS 2) is placed in pre¬ determined timeslots such that the configuration data intended for the second network element is in a pre¬ determined timeslot (308) and the configuration data intended for a third network element is in another time¬ slot (307) ; in the method the second network element (BTS 1) transfers the configuration data intended for the third network element (BTS 2) to said predetermined timeslot (403), the second network element transmits the con¬ figuration data intended for the third network element (BTS 2) to said third network element. 10. A data transmission method according to any one of the preceding claims, wherein the configuration data is transmitted over a transmission path on which the network elements (BSC, BTS 1, BTS 2) are located one after another, each part of the transmission path between two consecutive network elements forming one transmission link, c h a r a c t e r i z e d in that in each network element the configuration data is placed in a transmission frame in such a way that the config¬ uration data needed by the network element at the end of the following transmission link is in a predetermined fixed timeslot (308, 403). 11. A data transmission system in a cellular radio system, comprising as network elements a base station controller (BSC) and base stations (BTS 1, BTS 2) connected in series thereto via data transmission links; in the data transmission system, data is trans- mitted over said data transmission links in frames divided into timeslots; and the system is c h a r a c ¬ t e r i z e d in that the configuration data (308, 403) that is intended for the network elements and indicates in which timeslots of the frame the useful data intended for the network element (BTS 1, BTS 2) is carried is placed in a predetermined timeslot of the frame. 12. A data transmission system according to claim 11, c h a r a c t e r i z e d in that said con- figuration data is placed in the operation and mainten¬ ance channel transmitted over the data transmission link. 13. A data transmission system according to claim 11 or 12, c h a r a c t e r i z e d in that said configuration data is placed in the last timeslot of the frame of the data transmission link. 14. A data transmission system according to claim 11, 12 or 13, c h a r a c t e r i z e d in that said configuration data intended for each network element (BTS 1, BTS 2) is placed in a predetermined timeslot (308) of the frame for transmission to a first network element (BTS 1), and the configuration data indicating in which timeslot (303) of the data trans¬ mission link the useful data intended for the second network element is carried is placed in another timeslot (307) of the frame for transmission to the first network element (BTS 1), and the configuration data indicating in which timeslot of the data transmission link the useful data intended for the second network element is carried is placed in said predetermined timeslot (403) of the frame for transmission from the first network element (BTS 1) to a second network element (BTS 2).

Inventors: SUONVIERI JUKKA, SUONVIERI, JUKKA
Applicants: NOKIA TELECOMMUNICATIONS OY, SUONVIERI JUKKA, SUONVIERI, JUKKA
Application year: 1994
Main classification: H04J3
IPC codes: H04B7, H04J3, H04W24, H04W88, H04W92